This invention relates to the purification of butadiene streams, and, more particularly, to the removal of diethylhydroxylamine (DEHA) from butadiene streams.
Butadiene is a C4-unsaturated hydrocarbon that exists as two isomers. The 1,3-butadiene isomer is used in a variety of commercial applications, and is primarily used in the production of various polymers, such as styrene-butadiene rubber, polybutadiene, polychloroprene, nitrile rubber, acrylonitrile-butadiene-styrene, and styrene-butadiene latex. The 1,3-butadiene isomer is also used in the production of various chemicals, such as adiponitrile. By contrast, the thermodynamically less stable 1,2-butadiene isomer has virtually no commercial applications.
Butadiene may be manufactured using a variety of processes. In the past, butadiene was commonly prepared from acetylene or ethanol, or by the dehydrogenation of n-butane and oxydehydrogenation of n-butenes. Presently, butadiene is primarily produced as a by-product in the steam cracking of hydrocarbon streams to produce ethylene. Butadiene produced by steam cracking is typically then isolated from the other steam cracking by-products by fractional distillation and extractive distillation.
During butadiene isolation and separation, DEHA is commonly used as an inhibitor to prevent polymerization of the butadiene. Upon final isolation of the butadiene, DEHA is removed from the butadiene before it is used for commercial applications. Typically, DEHA is removed from the butadiene stream with a water wash, and then tert-butylcatechol (TBC) is added to the butadiene to prevent polymerization of the butadiene upon removal of the DEHA. However, using a water wash tends to cause the accumulation of an excessive amount of water in the isolated butadiene, which can interfere with subsequent applications of the butadiene. In addition, subsequent to its use, the water stream used in the water wash typically contains trace amounts of butadiene. Because the DEHA remaining in the water wash is difficult to isolate, the water stream must be properly disposed of, which can be costly because of the large volume of waste involved.
Therefore, what is needed is a method for removing DEHA from butadiene streams that does not leave an excessive amount of residual contaminates, such as water, in the isolated butadiene stream, and does not necessitate costly disposal fees.
Accordingly, the present invention is directed toward a method for removing DEHA from butadiene streams that does not leave an excessive amount of residual contaminates, such as water, in the isolated butadiene stream, and does not necessitate costly disposal fees. According to one embodiment of the present invention, DEHA is removed from butadiene streams by ion exchange resins. The use of ion exchange resins allows for the efficient removal of DEHA, without an accumulation of an excessive amount of residual contaminates. To prevent polymerization of the butadiene upon removal of the DEHA, TBC may be added to the butadiene stream before or after DEHA removal. After removal, the isolated DEHA can then be concentrated, and disposed or recycled.
In another embodiment, the present invention provides for the removal of DEHA from hydrocarbon streams by ion exchange resins.
In one embodiment, the present invention provides for a method of removing DEHA from butadiene streams. The method involves first providing a stream comprising primarily butadiene and a minor amount of DEHA. The stream is then contacted with an ion exchange resin to effectuate removal of the DEHA from the stream. After DEHA removal, a sufficient amount of TBC is added to the stream to prevent polymerization of the butadiene.
In another embodiment, the present invention provides for an alternate method of removing DEHA from butadiene streams. According to this method, a stream comprising primarily butadiene and a minor amount of DEHA is mixed with a sufficient amount of TBC to prevent polymerization of the butadiene upon removal of the DEHA. The stream is then contacted with an ion exchange resin to effectuate removal of the DEHA from the stream. Using this method, the ion exchange resin removes the DEHA, but does not remove a significant amount of TBC. As such, the butadiene stream remains inhibited during and after the DEHA removal process.
Typically, butadiene streams containing DEHA comprise primarily butadiene with a minor amount of DEHA. The term xe2x80x9cminor amountxe2x80x9d means that the butadiene/DEHA stream comprises less than about 100 ppm of DEHA. The term xe2x80x9cprimarily butadienexe2x80x9d means that the butadiene/DEHA stream comprises at least about 90% butadiene.
Preferably, the butadiene/DEHA stream is contacted with the ion exchange resin in a fixed bed reactor that has been charged with the ion exchange resin. However, the DEHA removal process may be conducted using a variety of other processing equipment to achieve substantially the same results.
Preferably, the ion exchange resin comprises a conventional acid resin. More preferably, the ion exchange resin comprises Amberlyst(copyright)-15, Amberlyst(copyright)-35, Amberlyst(copyright)-36, Amberlyst(copyright) XN-1010 (all from the Rohm and Haas Company), or Dowex(copyright)-50WX2 (from the Dow Chemical Company). Advantageously, the embodiments of the present invention are operable with fresh or spent resins. The term xe2x80x9cspent resinsxe2x80x9d refers to resins that have been used in other applications, and are no longer suitable for such applications because of the resin""s reduced activity. The spent resin may have been previously used in any number of applications, such as, but not limited to, the preparation of methyl-tert-butyl ether (MTBE), provided that such applications do not totally consume all of the active sites on the resin.
Preferably, the DEHA removal process should be conducted within a temperature range from about 0xc2x0 C. to about 110xc2x0 C. More preferably, the DEHA removal process should be conducted within a temperature range from about 15xc2x0 C. to about 50xc2x0 C.
Preferably, the DEHA removal process should be conducted at a pressure from about atmospheric pressure to about 2000 psig. More preferably, the DEHA removal process should be conducted at a pressure from about 50 psig to about 150 psig.
Preferably, if TBC is added to the butadiene stream before the DEHA is removed from the stream, a sufficient amount of TBC should be added so that before purification the stream contains at least about 5 ppm of TBC. If TBC is added to the butadiene stream after the DEHA is removed from the stream, a sufficient amount of TBC should be added to the effluent collection vessel so that the isolated butadiene stream contains at least about 5 ppm of TBC.
After removal from the butadiene stream, the isolated DEHA can then be concentrated, and disposed or recycled.
It is understood that several variations may be in the foregoing without departing from the scope of the invention. For instance, while the embodiments of the present invention are primarily discussed as being used to remove DEHA from butadiene streams, the present invention should not be construed as being limited to use with butadiene. The embodiments of the present invention may be used to remove DEHA from a variety of other hydrocarbons, or mixtures thereof. In most instances, the hydrocarbon will comprise an unsaturated hydrocarbon because DEHA is most often combined with such hydrocarbons to prevent their polymerization. In this embodiment, a stream comprising a hydrocarbon, or mixtures thereof, and a minor amount of DEHA, relative to the amount of the hydrocarbon in the stream, is contacted with an ion exchange resin to effectuate DEHA removal from the stream.
In addition, the embodiments of the present invention may be used in conjunction with other purification methods, including, but not limited to, the water wash method. If used in conjunction with another purification method, the embodiments of the present invention may be used prior to, or subsequent to, the other purification method(s). Other purification method(s) may be necessary to remove other residual impurities contained in the stream.